Setting the AuthDBMAuthoritative
directive explicitly to Off allows for both
authentication and authorization to be passed on to lower level
modules (as defined in the modules.c files) if there
is no userID or rule matching the
supplied userID. If there is a userID and/or rule specified; the
usual password and access checks will be applied and a failure will
give an "Authentication Required" reply.

So if a userID appears in the database of more than one module;
or if a valid Require
directive applies to more than one module; then the first module
will verify the credentials; and no access is passed on;
regardless of the AuthDBMAuthoritative
setting.

A common use for this is in conjunction with one of the
basic auth modules; such as mod_auth. Whereas this
DBM module supplies the bulk of the user credential checking; a
few (administrator) related accesses fall through to a lower
level with a well protected .htpasswd file.

By default, control is not passed on and an unknown userID
or rule will result in an "Authentication Required" reply. Not
setting it thus keeps the system secure and forces an NCSA
compliant behaviour.

Security:

Do consider the implications of allowing a user to allow
fall-through in his .htaccess file; and verify that this
is really what you want; Generally it is easier to just secure
a single .htpasswd file, than it is to secure a
database which might have more access interfaces.

The AuthDBMGroupFile directive sets the
name of a DBM file containing the list of user groups for user
authentication. File-path is the absolute path to the
group file.

The group file is keyed on the username. The value for a
user is a comma-separated list of the groups to which the users
belongs. There must be no whitespace within the value, and it
must never contain any colons.

Security: make sure that the
AuthDBMGroupFile is stored outside the
document tree of the web-server; do not put it in the
directory that it protects. Otherwise, clients will be able to
download the AuthDBMGroupFile unless
otherwise protected.

Combining Group and Password DBM files: In some cases it is
easier to manage a single database which contains both the
password and group details for each user. This simplifies any
support programs that need to be written: they now only have to
deal with writing to and locking a single DBM file. This can be
accomplished by first setting the group and password files to
point to the same DBM:

AuthDBMGroupFile /www/userbase
AuthDBMUserFile /www/userbase

The key for the single DBM is the username. The value consists
of

Unix Crypt-ed Password:List of Groups[:(ignored)]

The password section contains the encrypted password as before.
This is followed by a colon and the comma separated list of groups.
Other data may optionally be left in the DBM file after another colon;
it is ignored by the authentication module. This is what
www.telescope.org uses for its combined password and group database.

Sets the type of database file that is used to store the passwords.
The default database type is determined at compile time. The
availability of other types of database files also depends on
compile-time settings.

It is crucial that whatever program you use to create your password
files is configured to use the same type of database.

The AuthDBMUserFile directive sets the
name of a DBM file containing the list of users and passwords for
user authentication. File-path is the absolute path to
the user file.

The user file is keyed on the username. The value for a user is
the encrypted password, optionally followed by a colon and arbitrary
data. The colon and the data following it will be ignored by the
server.

Security:

Make sure that the AuthDBMUserFile is stored
outside the document tree of the web-server; do not put it in
the directory that it protects. Otherwise, clients will be able to
download the AuthDBMUserFile.

Important compatibility note: The implementation of
"dbmopen" in the apache modules reads the string length of the
hashed values from the DBM data structures, rather than relying
upon the string being NULL-appended. Some applications, such as
the Netscape web server, rely upon the string being
NULL-appended, so if you are having trouble using DBM files
interchangeably between applications this may be a part of the
problem.

A perl script called
dbmmanage is included with
Apache. This program can be used to create and update DBM
format password files for use with this module.